1. Field of the Invention
The invention relates to a hammer head adapted to be fixed to a hammer shaft, in particular a hammer head fitted with a claw for extracting nails from a work surface.
2. Prior Art
Claw hammers have been used for many years for extracting nails from a work surface. A claw hammer is particularly useful for removing nails from the work surface, because the hammer shaft provides leverage and thus a mechanical advantage which helps in overcoming resistance of the nail to being pulled from the surface. Difficulty can be experienced with a common claw hammer in extracting heavy long nails which have been driven so that the nail head thereof is flush with the work surface. This difficulty can be overcome by using a separate specialised nail puller with thin claws. Often long nails are bent when being extracted with a common claw hammer or nail puller.
Various devices have been invented to increase mechanical advantage of a claw hammer for extracting heavy long nails, and many of these devices relate to an adjustable fulcrum member or equivalent which increases mechanical advantage to facilitate extraction of such nails. Some of these adjustable fulcrums are hinged to the hammer head, and typical examples are found in U.S. Pat. No. 623,455 (Yonge); U.S. Pat. No. 2,231,206 (Anderson) and 2,657,903 (Johnson). While devices in some of these patents may be adequate for removing short or light nails, the fulcrum members of such patents are relatively weak when compared to the forces encountered in extracting long heavy nails, and such devices would likely fail under heavy usage. Many of the prior art devices use a relatively light flanged fulcrum member which is hinged to the hammer head by a relatively light pin. During extraction, extraction forces are transferred through the fulcrum member usually to the pin and through a relatively small bearing areas between the fulcrum member and the head. The pin and relatively small bearing areas are subjected to high bearing pressures, which result in rapid breakdown or wear of the surfaces, commonly with resulting premature failure of the device. Also, such fulcrum members commonly have an edge or corner which can be forced into the working surface during extraction, which edge results in high bearing forces applied to the work surface, causing indentation or other damage to the work surface.
Other nail extraction devices utilize longitudinally extending adjustable fulcrum members, typical devices being shown in U.S. Pat. No. 524,539 (Burgess); U.S. Pat. No. 1,067,729 (Frey) and U.S. Pat. No. 2,741,456 (Williams). The fulcrum member of each of these three patents extend from the hammer head outwardly in the direction of the hammer shaft, and have edges which would tend to be forced into the work surface during initial extraction of the nail, thus damaging the surface. Furthermore, the longitudinally extending fulcrum member is subjected to considerable lateral loads during initial extraction and likely would bend or wear excessively when subjected to heavy use.
Also, some of the fulcrum devices which are either hinged to the hammer head, or fitted for axial sliding movement relative the head, have a tendency to accidentally extend from the head during normal hammering. Also, some devices extend around side portions of the head and thus interfere with normal use of the hammer, and can prevent exceptional use of the hammer such as striking nails with the side of the hammer head which is sometimes required when driving nails in restricted spaces.